Fix api-coherence-checker agent job: switch to S2STOKENS authentication (#10223)

The `agent` job in the API Coherence Checker workflow was failing every
run with HTTP 401 because it depended on a `COPILOT_GITHUB_TOKEN`
repository secret that was missing/expired.

## Changes

- **`api-coherence-checker.lock.yml`**: Switch `agent` and `detection`
jobs from legacy `secrets.COPILOT_GITHUB_TOKEN` to the S2STOKENS
mechanism (service-to-service token exchange via the standard
`github.token`):

```yaml
# Before (agent and detection Execute Copilot CLI steps)
COPILOT_GITHUB_TOKEN: ${{ secrets.COPILOT_GITHUB_TOKEN }}
# no S2STOKENS

# After
COPILOT_GITHUB_TOKEN: ${{ github.token }}
S2STOKENS: true
```

- **Permissions**: Replace broad `permissions: read-all` on the `agent`
job (and add to `detection`) with minimal explicit scopes required for
S2STOKENS:
```yaml
permissions:
  contents: read
  copilot-requests: write  # required for S2STOKENS token exchange
```

This brings `api-coherence-checker` in line with the pattern already
used by `code-simplifier` and `release-notes-updater`.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

.github/workflows/api-coherence-checker.lock.yml

@@ -386,7 +386,9 @@ jobs:
     needs: activation
     if: needs.activation.outputs.daily_ai_credits_exceeded != 'true'
     runs-on: ubuntu-latest
-    permissions: read-all
+    permissions:
+      contents: read
+      copilot-requests: write
     concurrency:
       group: "gh-aw-copilot-${{ github.workflow }}"
       queue: max
@@ -818,7 +820,7 @@ jobs:
           AWF_REFLECT_ENABLED: 1
           COPILOT_AGENT_RUNNER_TYPE: STANDALONE
           COPILOT_DUMMY_BYOK: dummy-byok-key-for-offline-mode
-          COPILOT_GITHUB_TOKEN: ${{ secrets.COPILOT_GITHUB_TOKEN }}
+          COPILOT_GITHUB_TOKEN: ${{ github.token }}
           COPILOT_MODEL: ${{ vars.GH_AW_MODEL_AGENT_COPILOT || vars.GH_AW_DEFAULT_MODEL_COPILOT || 'claude-sonnet-4.6' }}
           GH_AW_LLM_PROVIDER: github
           GH_AW_MAX_AI_CREDITS: ${{ vars.GH_AW_DEFAULT_MAX_AI_CREDITS || '1000' }}
@@ -842,6 +844,7 @@ jobs:
           GIT_COMMITTER_EMAIL: github-actions[bot]@users.noreply.github.com
           GIT_COMMITTER_NAME: github-actions[bot]
           RUNNER_TEMP: ${{ runner.temp }}
+          S2STOKENS: true
           TRACEPARENT: ${{ env.GITHUB_AW_OTEL_TRACE_ID != '' && env.GITHUB_AW_OTEL_PARENT_SPAN_ID != '' && format('00-{0}-{1}-01', env.GITHUB_AW_OTEL_TRACE_ID, env.GITHUB_AW_OTEL_PARENT_SPAN_ID) || '' }}
       - name: Detect agent errors
         if: always()
@@ -1276,6 +1279,7 @@ jobs:
     runs-on: ubuntu-latest
     permissions:
       contents: read
+      copilot-requests: write
     env:
       GH_AW_RUNTIME_FEATURES: ${{ vars.GH_AW_RUNTIME_FEATURES }}
     outputs:
@@ -1438,7 +1442,7 @@ jobs:
           AWF_REFLECT_ENABLED: 1
           COPILOT_AGENT_RUNNER_TYPE: STANDALONE
           COPILOT_DUMMY_BYOK: dummy-byok-key-for-offline-mode
-          COPILOT_GITHUB_TOKEN: ${{ secrets.COPILOT_GITHUB_TOKEN }}
+          COPILOT_GITHUB_TOKEN: ${{ github.token }}
           COPILOT_MODEL: ${{ vars.GH_AW_MODEL_DETECTION_COPILOT || vars.GH_AW_DEFAULT_MODEL_COPILOT || 'claude-sonnet-4.6' }}
           GH_AW_LLM_PROVIDER: github
           GH_AW_MAX_AI_CREDITS: ${{ vars.GH_AW_DEFAULT_DETECTION_MAX_AI_CREDITS || '400' }}
@@ -1460,6 +1464,7 @@ jobs:
           GIT_COMMITTER_EMAIL: github-actions[bot]@users.noreply.github.com
           GIT_COMMITTER_NAME: github-actions[bot]
           RUNNER_TEMP: ${{ runner.temp }}
+          S2STOKENS: true
           TRACEPARENT: ${{ env.GITHUB_AW_OTEL_TRACE_ID != '' && env.GITHUB_AW_OTEL_PARENT_SPAN_ID != '' && format('00-{0}-{1}-01', env.GITHUB_AW_OTEL_TRACE_ID, env.GITHUB_AW_OTEL_PARENT_SPAN_ID) || '' }}
       - name: Parse threat detection token usage for step summary
         id: parse_detection_token_usage